U.S. patent application number 13/497248 was filed with the patent office on 2012-07-26 for method and apparatus for mode switching between a multi-cell coordinated communication mode and a single-cell mimo communication mode.
This patent application is currently assigned to LG ELECTRONICS INC.. Invention is credited to Byoung Hoon Kim, Han Byul Seo.
Application Number | 20120189077 13/497248 |
Document ID | / |
Family ID | 43876669 |
Filed Date | 2012-07-26 |
United States Patent
Application |
20120189077 |
Kind Code |
A1 |
Seo; Han Byul ; et
al. |
July 26, 2012 |
METHOD AND APPARATUS FOR MODE SWITCHING BETWEEN A MULTI-CELL
COORDINATED COMMUNICATION MODE AND A SINGLE-CELL MIMO COMMUNICATION
MODE
Abstract
A method for dynamically switching a communication mode includes
generating and transmitting first feedback information in
accordance with a first communication mode; switching the first
communication mode into a second communication mode interlocked
with the first communication mode; and generating and transmitting
second feedback information in accordance with the second
communication mode. The first communication mode is one of a
multi-cell coordinated multi-point (CoMP) communication mode and a
single-cell multi-input multi-output (MIMO) communication mode, and
the second communication mode is the other of the multi-cell
coordinated multi-point (CoMP) communication mode and the
single-cell multi-input multi-output (MIMO) communication mode. The
switching step can be performed without signaling from a base
station.
Inventors: |
Seo; Han Byul; (Anyang-si,
KR) ; Kim; Byoung Hoon; (Anyang-si, KR) |
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
43876669 |
Appl. No.: |
13/497248 |
Filed: |
October 5, 2010 |
PCT Filed: |
October 5, 2010 |
PCT NO: |
PCT/KR10/06792 |
371 Date: |
March 20, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61251670 |
Oct 14, 2009 |
|
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|
Current U.S.
Class: |
375/267 |
Current CPC
Class: |
H04B 7/0482 20130101;
H04B 7/024 20130101; H04B 7/0478 20130101; H04B 7/0689 20130101;
H04B 7/0632 20130101 |
Class at
Publication: |
375/267 |
International
Class: |
H04B 7/02 20060101
H04B007/02 |
Claims
1. A dynamic switching method of a communication mode, comprising:
generating and transmitting first feedback information according to
a first communication mode; switching from the first communication
mode to a second communication mode which has a corresponding
relationship with the first communication mode; and generating and
transmitting second feedback information according to the second
communication mode, wherein the first communication mode is one of
a multi-cell Coordinated Multi-Point (CoMP) communication mode and
a single-cell Multi-Input Multi-Output (MIMO) communication mode,
and the second communication mode is the other one except for the
first communication mode out of the CoMP communication mode and the
single-cell MIMO mode, and wherein the switching is performed
without relying on signaling from a base station.
2. The dynamic switching method of claim 1, wherein the
corresponding relationship of the first communication mode and the
second communication mode is configured between a CoMP
communication scheme supporting high rank transmission and a
single-cell MIMO communication scheme supporting high rank
transmission, and between a CoMP communication scheme supporting
low rank transmission and a single-cell MIMO communication scheme
supporting low rank transmission.
3. The dynamic switching method of claim 1, wherein the CoMP
communication scheme supporting high rank transmission and the
single-cell MIMO communication scheme supporting high rank
transmission are a CoMP Joint Transmission (JT) scheme and a
single-cell Single User (SU)-MIMO scheme, respectively, and wherein
the CoMP communication scheme supporting low rank transmission and
the single-cell MIMO communication scheme supporting low rank
transmission are a CoMP Coordinated Beamforming (CBF) scheme and a
single-cell Multi User (MU)-MIMO scheme, respectively.
4. The dynamic switching method of claim 1, wherein the first
feedback information and the second feedback information are
generated using the same feedback codebook.
5. The dynamic switching method of claim 1, wherein the first
feedback information is generated using a first feedback codebook,
the second feedback information is generated using a second
feedback codebook, and one of the first feedback codebook and the
second feedback codebook is composed of a subset of the other
one.
6. The dynamic switching method of claim 5, wherein a feedback
codebook used in the single-cell MIMO communication mode is
configured as a subset of a feedback codebook used in the CoMP
communication mode.
7. The dynamic switching method of claim 1, wherein feedback
information in the single-cell MIMO communication mode is a subset
of feedback information in the CoMP communication mode.
8. The dynamic switching method of claim 1, wherein when the
corresponding relationship of the first communication mode and the
second communication mode is configured between a CoMP JT scheme
and a single-cell SU-MIMO scheme, the first feedback information
and the second feedback information are generated using a feedback
codebook including unitary matrices.
9. The dynamic switching method of claim 1, wherein when the
corresponding relationship of the first communication mode and the
second communication mode is configured between a CoMP CBF scheme
and a single-cell MU-MIMO scheme, the first feedback information
and the second feedback information are generated using a feedback
codebook including non-unitary matrices.
10. The dynamic switching method of claim 1, wherein, when the
corresponding relationship of the first communication mode and the
second communication mode is configured between a CoMP CBF scheme
and a single-cell MU-MIMO scheme, the first feedback information
and the second feedback information are generated using a feedback
codebook having higher granularity than when the corresponding
relationship of the first communication mode and the second
communication mode is configured between a CoMP JT scheme and a
single-cell SU-MIMO scheme.
11. The dynamic switching method of claim 10, wherein the feedback
codebook having higher granularity is configured by a feedback
codebook of greater size, a hierarchical codebook, or an adaptive
codebook.
12. The dynamic switching method of claim 1, wherein the first
feedback information and the second feedback information are
generated based on the same hypothesis about Channel Quality
Indicator (CQI) calculation.
13. The dynamic switching method of claim 1, wherein the same MIMO
transmission scheme is used in the first communication mode and the
second communication mode.
14. A user equipment for dynamically switching communication modes,
comprising: a reception module for receiving a downlink signal from
a base station; a transmission module for transmitting an uplink
signal to the base station; and a processor for controlling the
user equipment including the reception module and the transmission
module, wherein the processor generates first feedback information
according to a first communication mode and generates second
feedback information according to a second communication mode,
transmits the first feedback information through the transmission
module when the user equipment operates in the first communication
mode and transmits the second feedback information through the
transmission module when the user equipment operates in the second
communication mode, and is configured to perform switching between
the first communication mode and the second communication mode,
wherein the first communication mode and the second communication
mode are communication modes having a corresponding relationship,
wherein the first communication mode is one of a multi-cell
Coordinated Multi-Point (CoMP) communication mode and a single-cell
Multi-Input Multi-Output (MIMO) communication mode, and the second
communication mode is the other one except for the first
communication mode out of the CoMP communication mode and the
single-cell MIMO mode, and wherein switching between the first
communication mode and the second communication mode is performed
without depending on signaling from a base station.
Description
TECHNICAL FIELD
[0001] The following description relates to a wireless
communication system, and more particularly, to a method and
apparatus for mode switching between a multi-cell coordinated
communication mode and a single-cell MIMO communication mode.
BACKGROUND ART
[0002] Multi-Input Multi-Output (MIMO) is a technique for improving
data transmission/reception efficiency using multiple transmit
antennas and multiple receive antennas, instead of employing one
transmit antenna and one receive antenna. When a single antenna is
used, a receiving side receives data through a single antenna path.
However, the receiving side receives data through multiple paths
when multiple antennas are used, and therefore, a data transmission
rate and data transmission amount can be improved and coverage can
be increased.
[0003] A single-cell MIMO operation may be divided into a Single
User-MIMO (SU-MIMO) scheme in which one User Equipment (UE)
receives a downlink signal in one cell and a Multi User-MIMO
(MU-MIMO) scheme in which two or more UEs receive a downlink signal
in one cell.
[0004] Meanwhile, much research into a Coordinated Multi-Point
(CoMP) system has been carried out to improve throughput of a user
located at a cell boundary by applying improved MIMO transmission
in a multi-cell environment. Application of the CoMP system can
reduce inter-cell interference in a multi-cell environment and can
improve overall system performance.
[0005] A CoMP scheme may be classified into, for example, a Joint
Processing (JP) scheme in which downlink data to be transmitted to
a specific UE is shared by all of CoMP coordinated cells and a
Coordinated BeamForming (CBF) scheme in which downlink data exists
only in one cell. The JP scheme may further be divided into a Joint
Transmission (JT) scheme in which all coordinated cells participate
in signal transmission and a Cooperative Silencing (CSL) scheme in
which only one cell participates in signal transmission and the
other cells stop transmitting signals to reduce interference. In
the CBF scheme, coordinated cells which do not transmit signals to
a UE may reduce inter-cell interference by way of determining a
beamforming matrix of the UE receiving signals therefrom so that
the corresponding UE is subject to less interference.
DETAILED DESCRIPTION OF THE INVENTION
Technical Problems
[0006] A multi-cell CoMP operation may be considered extension of a
single-cell MIMO operation. In other words, the multi-cell CoMP
operation may be regarded operation as a virtual MIMO system by
grouping a plurality of spatially separated BSs (or cells) into
one. From this viewpoint, a communication scheme of the multi-cell
CoMP operation has a close relationship with a communication scheme
of a single-cell MIMO operation. Considering this, it is an object
of the present invention to provide a method and apparatus for mode
switching between a multi-cell CoMP communication mode and a
single-cell MIMO communication mode.
[0007] It will be appreciated by persons skilled in the art that
that the technical objects that can be achieved through the present
invention are not limited to what has been particularly described
hereinabove and other technical objects of the present invention
will be more clearly understood from the following detailed
description.
Technical Solutions
[0008] To achieve the above technical object, a method for
dynamically switching a communication mode in accordance with an
embodiment of the present invention includes generating and
transmitting first feedback information according to a first
communication mode; switching from the first communication mode to
a second communication mode which has a corresponding relationship
with the first communication mode; and generating and transmitting
second feedback information according to the second communication
mode, wherein the first communication mode is one of a multi-cell
Coordinated Multi-Point (CoMP) communication mode and a single-cell
Multi-Input Multi-Output (MIMO) communication mode, and the second
communication mode is the other one except for the first
communication mode out of the CoMP communication mode and the
single-cell MIMO mode, and wherein the switching is performed
without relying on signaling from a base station.
[0009] The corresponding relationship of the first communication
mode and the second communication mode is configured between a CoMP
communication scheme supporting high rank transmission and a
single-cell MIMO communication scheme supporting high rank
transmission, and between a CoMP communication scheme supporting
low rank transmission and a single-cell MIMO communication scheme
supporting low rank transmission.
[0010] The CoMP communication scheme supporting high rank
transmission and the single-cell MIMO communication scheme
supporting high rank transmission are a CoMP Joint Transmission
(JT) scheme and a single-cell Single User (SU)-MIMO scheme,
respectively, and wherein the CoMP communication scheme supporting
low rank transmission and the single-cell MIMO communication scheme
supporting low rank transmission are a CoMP Coordinated Beamforming
(CBF) scheme and a single-cell Multi User (MU)-MIMO scheme,
respectively.
[0011] The first feedback information and the second feedback
information are generated using the same feedback codebook.
[0012] The first feedback information is generated using a first
feedback codebook, the second feedback information is generated
using a second feedback codebook, and one of the first feedback
codebook and the second feedback codebook is composed of a subset
of the other one.
[0013] A feedback codebook used in the single-cell MIMO
communication mode is configured as a subset of a feedback codebook
used in the CoMP communication mode.
[0014] Feedback information in the single-cell MIMO communication
mode is a subset of feedback information in the CoMP communication
mode.
[0015] When the corresponding relationship of the first
communication mode and the second communication mode is configured
between a CoMP JT scheme and a single-cell SU-MIMO scheme, the
first feedback information and the second feedback information are
generated using a feedback codebook including unitary matrices.
[0016] When the corresponding relationship of the first
communication mode and the second communication mode is configured
between a CoMP CBF scheme and a single-cell MU-MIMO scheme, the
first feedback information and the second feedback information are
generated using a feedback codebook including non-unitary
matrices.
[0017] When the corresponding relationship of the first
communication mode and the second communication mode is configured
between a CoMP CBF scheme and a single-cell MU-MIMO scheme, the
first feedback information and the second feedback information are
generated using a feedback codebook having higher granularity than
when the corresponding relationship of the first communication mode
and the second communication mode is configured between a CoMP JT
scheme and a single-cell SU-MIMO scheme.
[0018] The feedback codebook having higher granularity is
configured by a feedback codebook of greater size, a hierarchical
codebook, or an adaptive codebook.
[0019] The first feedback information and the second feedback
information are generated based on the same hypothesis about
Channel Quality Indicator (CQI) calculation.
[0020] The same MIMO transmission scheme is used in the first
communication mode and the second communication mode.
[0021] To achieve the above technical object, a user equipment for
dynamically switching communication modes in accordance with
another embodiment of the present invention includes a reception
module for receiving a downlink signal from a base station, a
transmission module for transmitting an uplink signal to the base
station, and a processor for controlling the user equipment
including the reception module and the transmission module, wherein
the processor generates first feedback information according to a
first communication mode and generates second feedback information
according to a second communication mode, transmits the first
feedback information through the transmission module when the user
equipment operates in the first communication mode and transmits
the second feedback information through the transmission module
when the user equipment operates in the second communication mode,
and is configured to perform switching between the first
communication mode and the second communication mode, wherein the
first communication mode and the second communication mode are
communication modes having a corresponding relationship, wherein
the first communication mode is one of a multi-cell Coordinated
Multi-Point (CoMP) communication mode and a single-cell Multi-Input
Multi-Output (MIMO) communication mode, and the second
communication mode is the other one except for the first
communication mode out of the CoMP communication mode and the
single-cell MIMO mode, and wherein switching between the first
communication mode and the second communication mode is performed
without depending on signaling from a base station.
[0022] The above-described general description of the present
invention and a detailed description thereof which will be
described are exemplary and are for additional description for
invention written in claims.
Advantageous Effects
[0023] According to the above-described aspects of the present
invention, dynamic mode switching between a multi-cell CoMP
communication mode and a single-cell MIMO communication mode can be
efficiently performed.
[0024] It will be appreciated by persons skilled in the art that
that the effects that can be achieved through the present invention
are not limited to what has been particularly described hereinabove
and other advantages of the present invention will be more clearly
understood from the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The accompanying drawings, which are included to provide a
further understanding of the invention, illustrate embodiments of
the invention and together with the description serve to explain
the principle of the invention. In the drawings:
[0026] FIG. 1 is a diagram conceptually illustrating a CoMP
operation of an intra eNB and an inter eNB;
[0027] FIG. 2 is a block diagram illustrating the structure of a
transmitter including multiple antennas;
[0028] FIG. 3 is a diagram illustrating the structure of a Type 1
radio frame;
[0029] FIG. 4 is a diagram illustrating the structure of a Type 2
radio frame;
[0030] FIG. 5 is a diagram illustrating an exemplary resource grid
for one downlink slot;
[0031] FIG. 6 is a diagram illustrating the structure of a downlink
subframe;
[0032] FIG. 7 is a diagram illustrating the structure of an uplink
subframe;
[0033] FIG. 8 is a diagram illustrating the configuration of a
radio communication system having multiple antennas;
[0034] FIG. 9 is a diagram explaining a basic concept of codebook
based precoding;
[0035] FIG. 10 is a diagram conceptually explaining a corresponding
relationship and switching operation between a CoMP communication
scheme and a single-cell MIMO communication scheme;
[0036] FIG. 11 is a flowchart of a dynamic switching method between
a CoMP communication mode and a single-cell MIMO communication mode
according to an exemplary embodiment of the present invention;
and
[0037] FIG. 12 is a diagram illustrating the configuration of an
exemplary embodiment of a UE according to the present
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0038] The following embodiments are achieved by combination of
structural elements and features of the present invention in a
predetermined manner. Each of the structural elements or features
should be considered selectively unless specified otherwise. Each
of the structural elements or features may be carried out without
being combined with other structural elements or features. Also,
some structural elements and/or features may be combined with one
another to constitute the embodiments of the present invention. The
order of operations described in the embodiments of the present
invention may be changed. Some structural elements or features of
one embodiment may be included in another embodiment, or may be
replaced with corresponding structural elements or features of
another embodiment.
[0039] In exemplary embodiments of the present invention, a
description is given of a data transmission and reception
relationship between a base station and a terminal. Here, the base
station refers to a terminal node of a network communicating
directly with the terminal. In some cases, a specific operation
described as being performed by the base station may be performed
by an upper node of the base station.
[0040] In other words, it is apparent that, in a network comprised
of a plurality of network nodes including a base station, various
operations performed for communication with a terminal may be
performed by the base station, or network nodes other than the base
station. The term `base station` may be replaced with terms such as
fixed station, Node B, eNode B (eNB), and Access Point (AP). Also,
in the following description, the term `base station` may be used
as a concept including a cell or a sector. For example, in the
present invention, a serving base station may be referred to as a
serving cell, and a coordinated base station may be referred to as
a coordinated cell. Also, the term `terminal` may be replaced with
terms such as User Equipment (UE), Mobile Station (MS), Mobile
Subscriber Station (MSS), and Subscriber Station (SS).
[0041] Specific terms disclosed in the present invention are
proposed to aid in understanding the present invention, and the use
of these specific terms may be changed to another format within the
technical scope or spirit of the present invention.
[0042] In some instances, well-known structures and devices may be
omitted in order to avoid obscuring the concepts of the present
invention and the important functions of the structures and devices
may be shown in block diagram form. The same reference numbers will
be used throughout the drawings to refer to the same or like
parts.
[0043] Exemplary embodiments of the present invention are supported
by standard documents disclosed in at least one of wireless access
systems including an Institute of Electrical and Electronics
Engineers (IEEE) 802 system, a 3.sup.rd Generation Partnership
Project (3GPP) system, a 3GPP Long Term Evolution (LTE) system, and
a 3GPP2 system. In particular, the steps or parts, which are not
described to clearly reveal the technical idea of the present
invention, in the embodiments of the present invention may be
supported by the above documents. All terminology used herein may
be supported by the above-mentioned documents.
[0044] The following technique can be used for a variety of radio
access systems, for example, Code Division Multiple Access (CDMA),
Frequency Division Multiple Access (FDMA), Time Division Multiple
Access (TDMA), Orthogonal Frequency Division Multiple Access
(OFDMA), Single Carrier Frequency Division Multiple Access
(SC-FDMA), and the like. CDMA may be embodied through radio
technology such as Universal Terrestrial Radio Access (UTRA) or
CDMA2000. TDMA may be embodied through radio technology such as
Global System for Mobile communications (GSM)/General Packet Radio
Service (GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA
may be embodied through radio technology such as Institute of
Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE
802.16 (WiMAX), IEEE 802-20, and E-UTRA (Evolved UTRA). UTRA is a
part of the Universal Mobile Telecommunications System (UMTS). 3GPP
LTE is a part of the E-UMTS (Evolved UMTS), which uses E-UTRA. 3GPP
LTE employs OFDMA in downlink and employs SC-FDMA in uplink. LTE-A
is an evolved version of 3GPP LTE. WiMAX can be explained by an
IEEE 802.16e (WirelessMAN-OFDMA Reference System) and an advanced
IEEE 802.16m (WirelessMAN-OFDMA Advanced System). For clarity, the
following description focuses on the 3GPP LTE and LTE-A systems.
However, technical features of the present invention are not
limited thereto.
[0045] A Coordinated Multi-Point (CoMP) system will now be
described with reference to FIG. 1. FIG. 1 is a diagram
conceptually illustrating a CoMP operation of an intra eNB and an
inter eNB.
[0046] Referring to FIG. 1, there are intra eNBs 110 and 120 and an
inter eNB 130 in a multi-cell environment. In an LTE system, an
intra eNB includes several cells (or sectors). Cells covered by an
eNB to which a specific UE belongs are in an intra eNB (110 or 120)
relationship with the specific UE. In other words, cells sharing
the same eNB as an eNB managing a cell to which a UE belongs are
cells corresponding to the intra eNB 110 or 120, whereas cells
under different eNBs are cells corresponding to the inter eNB 130.
Cells (i.e. intra eNB) based on the same eNB as an eNB to which a
specific UE belongs exchange information (e.g. data and Channel
State information (CSI)) with each other without an additional
interface between schedulers of the respective cells. Cells (i.e.
inter eNB) in different eNBs exchange information between the cells
through a backhaul 140. As illustrated in FIG. 1, a single-cell
MIMO user 150 in a single cell may communicate with one serving eNB
in one cell (Cell A, Cell B, Cell C, Cell D, or Cell E), and a
multi-cell MIMO user 160 located at a cell boundary may communicate
with a plurality of serving eNBs in multiple cells (Cell A and Cell
B, or Cell B, Cell C and Cell D).
[0047] A CoMP system refers to a system for improving throughput of
a user located at a cell boundary by applying improved MIMO
transmission in a multi-cell environment. If the CoMP system is
applied, it is possible to reduce inter-cell interference in a
multi-cell environment.
[0048] The CoMP scheme may be classified into, for example, a Joint
Processing (JP) scheme in which downlink data to be transmitted to
a specific UE is shared by all of CoMP coordinated cells and a
Coordinated Beamforming (CBF) scheme in which downlink data exists
only in one cell. The JP scheme may further be divided into a Joint
Transmission (JT) scheme in which all coordinated cells participate
in signal transmission and a Cooperative Silencing (CSL) scheme in
which only one cell participates in signal transmission and the
other cells stop transmitting signals to reduce interference. In
the CBF scheme, coordinated cells which do not transmit signals to
a UE can reduce inter-cell interference by determining a
beamforming matrix of a UE receiving signals therefrom so that the
corresponding UE is subject to less interference.
[0049] If such a CoMP system is used, a UE may commonly receive
data from multi-cell eNBs. In addition, the eNBs may simultaneously
support one or more UEs using the same radio frequency resource to
improve system performance. Also, the eNB may perform a Space
Division Multiple Access (SDMA) method based on CSI between the eNB
and the UE.
[0050] In the CoMP system, a serving eNB and one or more
coordinated eNBs are connected to a scheduler via a backbone
network. The scheduler may operate by receiving channel information
about a channel status between each UE and coordinated eNBs through
the backbone network, measured by each eNB. For example, the
scheduler may schedule information for a coordinated MIMO operation
with respect to a serving eNB and one or more coordinated eNBs. In
other words, the scheduler may directly command each eNB to perform
a coordinated MIMO operation.
[0051] As described above, the CoMP system may be considered a
virtual MIMO system by grouping a plurality of neighboring cells
into one and a communication scheme of a MIMO system using multiple
antennas may be basically applied thereto. Operation of the MIMO
system will be described in detail later.
[0052] FIG. 2 is a block diagram illustrating the structure of a
transmitter including multiple antennas.
[0053] Referring to FIG. 2, a transmitter 200 includes encoders
210-1, . . . , 210-K, modulation mappers 220-1, . . . , 220-K, a
layer mapper 230, a precoder 240, resource element mappers 250-1, .
. . , 250-K, and OFDM signal generators 260-1, . . . , 260K. The
transmitter 200 further includes Nt transmit antennas 270-1, . . .
, 270-Nt.
[0054] The encoders 210-1, . . . , 210-K form coded data by
encoding input data according to a predetermined coding scheme. The
modulation mappers 220-1, . . . , 220-K map the coded data to
modulation symbols indicating locations on a signal constellation.
The modulation scheme may be, but not limited to, any of m-Phase
Shift Keying (m-PSK) and m-Quadrature Amplitude Modulation (m-QAM).
The m-PSK may be BPSK, QPSK, or 8-PSK for example. The m-QAM may be
16-QAM, 64-QAM, or 256-QAM.
[0055] The layer mapper 230 defines the layers of the modulation
symbols so that the precoder 240 can distribute antenna-specific
symbols to paths of the respective antennas. A layer is defined as
an information path input to the precoder 240. An information path
prior to the precoder 240 may be called a virtual antenna or
layer.
[0056] The precoder 240 processes the modulation symbols by a MIMO
scheme according to the multiple transmit antennas 270-1, . . . ,
270-Nt and outputs the antenna-specific symbols. The precoder 240
distributes the antenna-specific symbols to the resource element
mappers 250-1, . . . , 250-K of corresponding antenna paths. Each
information path transmitted to one antenna by the precoder 240 is
called a stream. The stream may also be called a physical
antenna.
[0057] The resource element mappers 250-1, . . . , 250-K allocate
the antenna-specific symbols to proper resource elements and
multiplex the antenna-specific symbols according to users. The OFDM
signal generators 260-1, . . . , 260-K modulate the
antenna-specific symbols according to an OFDM scheme and generate
OFDM symbols. The OFDM signal generators 260-1, . . . , 260-K may
perform Inverse Fast Fourier Transform (IFFT) upon the
antenna-specific symbols. A Cyclic Prefix (CP) may be inserted into
time domain symbols upon which IFFT has been performed. The CP is a
signal inserted to a guard interval in order to eliminate
inter-symbol interference caused by multiple paths in an OFDM
transmission scheme. The OFDM symbols are transmitted through the
respective transmit antennas 270-1, . . . , 270-Nt.
[0058] The structure of a radio frame will now be described with
reference to FIG. 3 and FIG. 4.
[0059] In a cellular OFDM radio packet communication system,
uplink/downlink data packet transmission is performed in subframe
units. One subframe is defined as a predetermined time interval
including a plurality of OFDM symbols. The 3GPP LTE standard
supports a type 1 radio frame structure applicable to Frequency
Division Duplex (FDD) and a type 2 radio frame structure applicable
to Time Division Duplex (TDD).
[0060] FIG. 3 is a diagram illustrating the structure of the type 1
radio frame. A downlink radio frame includes 10 subframes, and one
subframe includes two slots. A time required to transmit one
subframe is defined as a Transmission Time Interval (TTI). For
example, one subframe may have a length of 1 ms and one slot may
have a length of 0.5 ms. One slot may include a plurality of OFDM
symbols in the time domain and include a plurality of Resource
Blocks (RBs) in the frequency domain.
[0061] The number of OFDM symbols included in one slot may be
changed according to the configuration of a CP. The CP includes an
extended CP and a normal CP. For example, if the OFDM symbols are
configured by the normal CP, the number of OFDM symbols included in
one slot may be seven. If the OFDM symbols are configured by the
extended CP, since the length of one OFDM symbol is increased, the
number of OFDM symbols included in one slot is less than that of
the case of the normal CP. In case of the extended CP, for example,
the number of OFDM symbols included in one slot may be six. If a
channel state is unstable, for example, if a UE moves at a high
speed, the extended CP may be used in order to further reduce
inter-symbol interference.
[0062] In case of using the normal CP, since one slot includes 7
OFDM symbols, one subframe includes 14 OFDM symbols. At this time,
the first two or three OFDM symbols of each subframe may be
allocated to a Physical Downlink Control Channel (PDCCH) and the
remaining OFDM symbols may be allocated to a Physical Downlink
Shared Channel (PDSCH).
[0063] FIG. 4 is a diagram illustrating the structure of the type 2
radio frame. The type 2 radio frame includes two half frames, each
of which includes five subframes. The subframes may be classified
into general subframes and special subframes. The special subframe
includes three fields of a Downlink Pilot Time Slot (DwPTS), a
Guard Period (GP), and an Uplink Pilot Time Slot (UpPTS). Although
the lengths of these three fields may be individually configured, a
total length of the three fields should be 1 ms. One subframe
includes two slots. In other words, one subframe includes two slots
regardless of a type of the radio frame.
[0064] The structure of the radio frame is only exemplary.
Accordingly, the number of subframes included in the radio frame,
the number of slots included in the subframe, or the number of
symbols included in the slot may be changed in various manners.
[0065] FIG. 5 is a diagram illustrating an exemplary resource grid
for one downlink slot. In FIG. 5, OFDM symbols are configured by a
normal CP. Referring to FIG. 5, a downlink slot includes a
plurality of OFDM symbols in the time domain and a plurality of RBs
in the frequency domain. Although one downlink slot includes 7 OFDM
symbols and one RB includes 12 subcarriers in the figure, the
numbers of OFDM symbols and subcarriers are not limited thereto.
Each element on the resource grid is referred to as a Resource
Element (RE). For example, an RE a(k,l) denotes an RE located in a
k-th subcarrier and an l-th OFDM symbol. In case of a normal CP,
one RB includes 12.times.7 REs (in case of an extended CP, one RB
includes 12.times.6 REs). Since each subcarrier spacing is 15 kHz,
one RB includes about 180 kHz in the frequency domain. N.sup.DL
denotes the number of RBs included in the downlink slot. A value of
N.sup.DL may be determined based on a downlink transmission
bandwidth which is configured by scheduling of an eNB.
[0066] FIG. 6 is a diagram illustrating the structure of a downlink
subframe. A maximum of three OFDM symbols (one, two, or three OFDM
symbols) of a front portion of a first slot within one subframe
corresponds to a control region to which a control channel is
allocated. The remaining OFDM symbols correspond to a data region
to which a Physical Downlink Shared Channel (PDSCH) is allocated. A
basic transmission unit is one subframe. Namely, a PDCCH and a
PDSCH are allocated over two slots. Examples of the downlink
control channels used in the 3GPP LTE system include a Physical
Control Format Indicator Channel (PCFICH), a Physical Downlink
Control Channel (PDCCH), a Physical Hybrid automatic repeat request
Indicator Channel (PHICH), etc. The PCFICH is transmitted at a
first OFDM symbol of a subframe, and includes information about the
number of OFDM symbols used to transmit the control channel in the
subframe. The PHICH includes a HARQ ACK/NACK signal as a response
to uplink transmission. The control information transmitted through
the PDCCH is referred to as Downlink Control Information (DCI). The
DCI includes uplink or downlink scheduling information or an uplink
transmit power control command for a certain UE group. The PDCCH
may include resource allocation and transmission format of a
Downlink Shared Channel (DL-SCH), resource allocation information
of an Uplink Shared Channel (UL-SCH), paging information of a
Paging Channel (PCH), system information on the DL-SCH, resource
allocation of a higher layer control message such as a random
access response transmitted on the PDSCH, a set of transmit power
control commands for individual UEs in a certain UE group, transmit
power control information, activation of Voice over IP (VoIP), etc.
A plurality of PDCCHs may be transmitted within the control region.
The UE may monitor the plurality of PDCCHs. The PDCCHs are
transmitted on an aggregation of one or several consecutive Control
Channel Elements (CCEs). The CCE is a logical allocation unit used
to provide the PDCCHs at a coding rate based on the state of a
radio channel. The CCE corresponds to a plurality of RE groups. The
format of the PDCCH and the number of available bits are determined
based on a correlation between the number of CCEs and a coding rate
provided by the CCEs. An eNB determines a PDCCH format according to
DCI transmitted to a UE, and attaches a Cyclic Redundancy Check
(CRC) to control information. The CRC is masked with an identifier
called a Radio Network Temporary Identifier (RNTI) according to an
owner or usage of the PDCCH. If the PDCCH is for a specific UE, a
Cell-RNTI (C-RNTI) of the UE may be masked to the CRC.
Alternatively, if the PDCCH is for a paging message, a paging
indicator identifier (P-RNTI) may be masked to the CRC. If the
PDCCH is for system information (more specifically, a System
Information Block (SIB)), a system information identifier and a
System Information RNTI (SI-RNTI) may be masked to the CRC. To
indicate a random access response that is a response for
transmission of a random access preamble of a UE, a Random
Access-RNTI (RA-RNTI) may be masked to the CRC.
[0067] FIG. 7 is a diagram illustrating the structure of an uplink
frame. The uplink subframe may be divided into a control region and
a data region in the frequency domain. A Physical Uplink Control
Channel (PUCCH) including uplink control information is allocated
to the control region. A Physical Uplink Shared Channel (PUSCH)
including user data is allocated to the data region. The PUCCH is
used for three broadly divided purposes: ACK/NACK transmission for
the PDSCH, Channel Quality Indicator (CQI) transmission for
frequency domain scheduling of the PDSCH, and PUSCH transmission
resource request (scheduling request). A CQI information bit may
include one or more fields. For example, a CQI field indicating a
CQI index for determining a Modulation and Coding Scheme (MCS), a
Precoding Matrix Indicator (PMI) field indicating a precoding
matrix index in a codebook, and a Rank Indicator (RI) field
indicating a rank may be included in the CQI information bit.
[0068] To maintain single carrier property, one UE does not
simultaneously transmit the PUCCH and the PUSCH. The PUCCH for one
UE is allocated to an RB pair in a subframe. RBs belonging to the
RB pair occupy different subcarriers over two slots. This is
considered that the RB pair allocated to the PUCCH is
frequency-hopped at a slot boundary.
[0069] MIMO System
[0070] FIG. 8 illustrates the configuration of a radio
communication system having multiple antennas. As shown in FIG.
8(a), if the number of transmit antennas is increased to N.sub.T
and the number of receive antennas is increased to N.sub.R, a
theoretical channel transmission capacity is increased in
proportion to the number of antennas, unlike the case where a
plurality of antennas is used in either a transmitter or a
receiver. Accordingly, it is possible to improve transmission rate
and to remarkably improve frequency efficiency. As the channel
transmission capacity is increased, the transmission rate may be
theoretically increased by a product of a maximum transmission rate
R.sub.0 upon using a single antenna and a rate increase ratio
R.sub.i.
R.sub.i=min(N.sub.T, N.sub.R) Equation 1
[0071] For example, in a MIMO system using four transmit antennas
and four receive antennas, it is possible to theoretically acquire
a transmission rate which is four times that of a single antenna
system. After the increase in the theoretical capacity of the MIMO
system was proven in the mid-1990s, various technologies for
substantially improving data transmission rate have been actively
developed up to now. In addition, several technologies have already
been applied to the various radio communication standards such as
the third-generation mobile communication and the next-generation
wireless local area network (LAN).
[0072] According to research trends in MIMO up to now, research has
been actively conducted in various aspects, such as research into
information theory related to MIMO communication capacity
calculation in various channel environments and multiple access
environments, research into radio channel measurement and model
derivation of the MIMO system, and research into space-time signal
processing technologies for improving transmission reliability and
transmission rate.
[0073] The communication method of the MIMO system will be
described in more detail using mathematical modeling. In the above
system, it is assumed that N.sub.T transmit antennas and N.sub.R
receive antennas are present.
[0074] In transmission signals, if N.sub.T transmit antennas are
present, the number of pieces of maximally transmittable
information is N.sub.T. The transmission information may be
expressed as follows.
s=.left brkt-bot.s.sub.1, s.sub.2, . . . , s.sub.NT.sub.T.right
brkt-bot..sup.T Equation 2
[0075] The transmission information S.sub.1, S.sup.2, . . . ,
S.sub.N.sub.T may have different transmit powers. If the respective
transmit powers are P.sub.1, P.sub.2, P.sub.N.sub.T, the
transmission information with adjusted powers may be expressed as
follows.
s=[s.sub.1, s.sub.2, . . . , s.sub.N.sub.T].sup.T=[P.sub.1s.sub.1,
P.sub.2s.sub.2, . . . , P.sub.N.sub.Ts.sub.N.sub.T].sup.T Equation
3
[0076] In addition, S may be expressed using a diagonal matrix P of
the transmit powers as follows.
s ^ = [ P 1 0 P 2 0 P N T ] [ s 1 s 2 s N T ] = Ps Equation 4
##EQU00001##
[0077] Consider that the N.sub.T actually transmitted signals
x.sub.1, x.sub.2, . . . , x.sub.N.sub.T are configured by applying
a weight matrix W to the information vector S with the adjusted
transmit powers. The weight matrix W serves to appropriately
distribute the transmission information to each antenna according
to a transport channel state, etc. x.sub.1, x.sub.2, . . . ,
x.sub.N.sub.T may be expressed by using the vector X as
follows.
x = [ x 1 x 2 x i x N T ] = [ w 11 w 12 w 1 N T w 21 w 22 w 2 N T w
i 1 w i 2 w iN T w N T 1 w N T 2 w N T N T ] [ s ^ 1 s ^ 2 s ^ j s
^ N T ] = W s ^ = WPs Equation 5 ##EQU00002##
[0078] where, W.sub.ij denotes a weight between an i-th transmit
antenna and j-th information. W is also called a precoding
matrix.
[0079] If the N.sub.R receive antennas are present, respective
reception signals y.sub.1, y.sub.2, . . . , y.sub.N.sub.R of the
antennas are expressed as follows.
y=[y.sub.1, y.sub.2, . . . , y.sub.N.sub.R].sup.T Equation 6
[0080] If channels are modeled in the MIMO radio communication
system, the channels may be distinguished according to
transmit/receive antenna indexes. A channel from the transmit
antenna j to the receive antenna i is denoted by i. In h.sub.ij. In
h.sub.ij, it is noted that the indexes of the receive antennas
precede the indexes of the transmit antennas in view of the order
of indexes.
[0081] FIG. 8(b) illustrates channels from the N.sub.T transmit
antennas to the receive antenna i. The channels may be combined and
expressed in the form of a vector and a matrix. In FIG. 8(b), the
channels from the N.sub.T transmit antennas to the receive antenna
i may be expressed as follows.
h.sub.i.sup.T=[h.sub.i1, h.sub.i2, . . . , h.sub.iN.sub.T] Equation
7
[0082] Accordingly, all the channels from the N.sub.T transmit
antennas to the N.sub.R receive antennas may be expressed as
follows.
H = [ h 1 T h 2 T h i T h N R T ] = [ h 11 h 12 h 1 N T h 21 h 22 h
2 N T h i 1 h i 2 h iN T h N R 1 h N R 2 h N R N T ] Equation 8
##EQU00003##
[0083] Additive White Gaussian Noise (AWGN) is added to the actual
channels after a channel matrix H. The AWGN n.sub.1, n.sub.2, . . .
, n.sub.N.sub.R added to the N.sub.T transmit antennas may be
expressed as follows.
n=[n.sub.1, n.sub.2, . . . , n.sub.N.sub.R].sup.T Equation 9
[0084] Through the above-described mathematical modeling, the
reception signals may be expressed as follows.
y = [ y 1 y 2 y i y N R ] = [ h 11 h 12 h 1 N T h 21 h 22 h 2 N T h
i 1 h i 2 h iN T h N R 1 h N R 2 h N R N T ] [ x 1 x 2 x j x N T ]
+ [ n 1 n 2 n i n N R ] = Hx + n Equation 10 ##EQU00004##
[0085] The numbers of rows and columns of the channel matrix H
indicating the channel state are determined by the number of
transmit and receive antennas. The number of rows of the channel
matrix H is equal to the number N.sub.R of receive antennas and the
number of columns thereof is equal to the number N.sub.T of
transmit antennas. That is, the channel matrix H is an
N.sub.R.times.N.sub.T matrix.
[0086] The rank of the matrix is defined by the smaller of the
numbers of rows and columns which are independent of each other.
Accordingly, the rank of the matrix is not greater than the number
of rows or columns. The rank rank(H) of the channel matrix H is
restricted as follows.
rank(H).ltoreq.min(N.sub.T, N.sub.r) Equation 11
[0087] When the matrix is subjected to Eigen value decomposition,
the rank may be defined by the number of Eigen values excluding 0.
Similarly, when the matrix is subjected to singular value
decomposition, the rank may be defined by the number of singular
values excluding 0. Accordingly, the physical meaning of the rank
in the channel matrix may be a maximum number of different
transmittable information in a given channel.
[0088] In a description of the present document, a `rank` for MIMO
transmission refers to the number of paths which can independently
transmit signals in a specific time point and a specific frequency
resource, and `the number of layers` refers to the number of signal
streams transmitted to the respective paths. Generally, since a
transmitting end transmits layers corresponding in number to ranks
used for signal transmission, rank has the same meaning as the
number of layers unless particularly mentioned.
[0089] In a MIMO system, there are various MIMO transmission
schemes (transmission modes). A multiple antenna transmission and
reception scheme used for operation of the MIMO system may include
Frequency Switched Transmit Diversity (FSTD), Space Frequency Block
Code (SFBC), Space Time Block Code (STBC), Cyclic Delay Diversity
(CDD), Time Switched Transmit Diversity (TSTD), etc. In case of a
rank 2 or higher ranks, Spatial Multiplexing (SM), Generalized
Cyclic Delay Diversity (GCDD), Selective Virtual Antenna
Permutation (S-VAP), etc. may be used.
[0090] FSTD is a scheme for allocating subcarriers of different
frequencies to signals transmitted through multiple antennas to
obtain a diversity gain. SFBC is a scheme for efficiently applying
selectivity in the space domain and frequency domain to ensure both
a diversity gain in a corresponding dimension and a multi-user
scheduling gain. STBC is a scheme for applying selectivity in the
space domain and time domain. CDD is a scheme using a path delay
between transmit antennas to obtain a diversity gain. TSTD is a
scheme in which signals transmitted to multiple antennas are
divided based on time. SM is a scheme for transmitting different
data to each antenna to improve transmission rate. GCDD is a scheme
for applying selectivity in the time domain and frequency domain.
S-VAP is a scheme using a single precoding matrix, and includes a
Multi-Codeword (MCW) S-VAP for mixing multiple codewords to
antennas in spatial diversity or spatial multiplexing and a Single
Codeword (SCW) S-VAP using a single codeword.
[0091] According to the aforementioned various MIMO transmission
schemes (MIMO transmission modes), various types of scheduling
signaling (PDCCH DCI formats) may be used. In other words,
scheduling signaling may have various MIMO transmission modes in
different forms, and a UE may determine a MIMO transmission mode
according to the scheduling signaling.
[0092] Meanwhile, in the MIMO system, there are an open-loop scheme
in which feedback information from a receiving end is not used and
a closed-loop scheme in which feedback information from the
receiving end is used. The closed-loop scheme causes the receiving
end to transmit feedback information about a channel state to the
transmitting end and thus causes the transmitting end to recognize
the channel state, thereby improving the performance of a radio
communication system. The closed-loop MIMO system uses a precoding
scheme in which the transmitting end processes transmission data
using feedback information about a channel environment transmitted
from the receiving end to minimize the influence of a channel.
[0093] The precoding scheme includes a codebook based precoding
scheme and a precoding scheme for quantizing channel information
and then feeding back the quantized channel information.
[0094] In relation to the aforementioned MIMO transmission
technique, the codebook based precoding scheme is described. FIG. 9
is a diagram explaining a basic concept of codebook based
precoding.
[0095] In accordance with the codebook based precoding scheme, a
transmitter and a receiver share codebook information including a
predetermined number of precoding matrices according to a
transmission rank, the number of antennas, etc. The receiver may
measure a channel state through a received signal to feed back
preferred precoding matrix information (precoding matrix index)
based on the codebook information to the transmitter. In FIG. 9,
the receiver transmits preferred precoding matrix information to
the transmitter with respect to each codeword but the preferred
precoding matrix information is not limited thereto.
[0096] The transmitter receiving the feedback information from the
receiver may select a precoding matrix from a codebook based on the
received information. The transmitter selecting the precoding
matrix performs precoding by multiplying the selected precoding
matrix by layer signals corresponding in number to a transmission
rank and may transmit the precoded transmission signals through a
plurality of antennas. The receiver receiving the transmission
signals precoded by the transmitter may perform inverse processing
of precoding which has performed by the transmitter to restore
reception signals. Generally, the precoding matrix satisfies a
unitary matrix (U) condition such as U*U.sup.H=I. The
aforementioned inverse processing of precoding may be performed by
multiplying a Hermit matrix P.sup.H of the precoding matrix P used
for precoding of the transmitter by the reception signals.
[0097] Thus, since only a codebook based index is fed back to the
transmitter, system overhead can be greatly reduced compared with
feeding back all channel information.
[0098] Using the above codebook based precoding scheme, a scheme in
which a receiver (UE) feeds back channel information to a
transmitter (BS) in a multi-cell environment may be applied even to
a CoMP system.
[0099] More specifically, for effective operation of the CoMP
system, it is necessary to feed back, from the UE to the BS,
information such as a Precoding Matrix Index (PMI) of a virtual
multi-antenna channel formed between coordinated BSs and UEs
belonging to a coordinated group, Signal-to-Noise Ratio (SNR) (or
Signal-to-Interference plus Noise Ratio (SINR)) of each stream, and
the number of transmittable independent data (i.e. rank
information).
[0100] As a feedback scheme of a UE for channel information
necessary for a CoMP operation, an extended scheme of a channel
information feedback scheme used in conventional single-cell MIMO
communication may be considered. In other words, a UE may quantize
channel information of a coordinated BS using a single codebook
which fixedly uses a PMI of a channel of one BS, an SNR, the number
of bits for indicating a rank and then may feed back the quantized
channel information to the BS.
[0101] For example, if the UE feeds back an SNR and inter-cell
interference information to the BS, neighboring BSs may determine a
coordinated unit and a coordinated communication scheme using the
feedback information and may transmit the result to the UE. The UE
quantizes channel information of a coordinated BS using a single
codebook which fixedly uses a PMI of a channel of one BS, an SNR,
the number of bits for indicating rank and, if necessary, further
quantizes phase difference information of a channel of each BS to
feed back the quantized information to the BS. Then the BS may
perform inter-cell coordinated communication using the information
fed back by the UE.
[0102] Meanwhile, in order for a scheduler of a BS to select a
proper one of various coordinated transmission schemes, it is
necessary to consider distribution of users (UEs) and the number of
bits of a feedback quantized channel.
[0103] To determine an efficient coordinated transmission scheme,
feedback using a single level codebook from the UE may be
considered. According to this scheme, under the circumstance that
the BS and the UE share the same codebook of a single level, the BS
may transmit a reference signal or a pilot signal, and the UE may
estimate a channel using the reference signal, quantize channel
information about a selected subband, and feed back the quantized
channel information using a quantized bit of a single level to the
BS. The BS may perform coordinated transmission mode determination
and user scheduling using the feedback information and transmit the
data to a selected user. The UE may then transmit ACK/NACK
information about data transmission from the BS.
[0104] Mode Switching Method Between CoMP Communication Mode and a
Single-Cell MIMO Communication Mode
[0105] As described previously, the multi-cell CoMP communication
scheme can be divided into a JP scheme and a CBF scheme, and the JP
scheme includes JT and CSL. Meanwhile, the single-cell MIMO scheme
can be divided into an SU-MIMO scheme and an MU-MIMO scheme.
[0106] Since a multi-cell CoMP operation may be regarded operation
of a virtual MIMO system by grouping a plurality of spatially
separated BSs (or cells) into one, a communication scheme of the
multi-cell CoMP operation has a close relationship with a
communication scheme of a single-cell MIMO operation. In
consideration of this, the present invention proposes a method for
mode switching between a multi-cell CoMP communication mode and a
single-cell MIMO communication mode. More specifically, proper
communication schemes to which dynamic mode switching is applicable
(i.e. having a corresponding relationship) between a multi-cell
CoMP communication mode and a single-cell MIMO communication mode
will be discussed, and methods for dynamic switching between the
communication schemes having the corresponding relationship, and
detailed proposal matters for supporting the dynamic switching
methods will be described.
[0107] CoMP Communication Scheme and Single-Cell MIMO Communication
Scheme Having a Corresponding Relationship
[0108] The CoMP communication scheme and the single-cell MIMO
communication scheme may have a corresponding relationship with
each other based on rank. Here, rank refers to the number of data
layers which are simultaneously transmitted to one UE in a specific
time point and a specific frequency resource.
[0109] As an example, JT of the CoMP communication scheme and
SU-MIMO of the single-cell MIMO communication scheme have something
in common in that the both schemes generally perform transmission
of a high rank. More specifically, in case of the CoMP JT scheme,
two or more cells participate in transmission for one UE and,
therefore, there is a high probability of high rank transmission.
In case of the single-cell SU-MIMO scheme, one UE utilizes all
spatial resources of one cell and, therefore, there is a high
probability of high rank transmission. Accordingly, the
corresponding relationship between the CoMP JT scheme and the
single-cell SU-MIMO scheme may be considered based on a common
point of high rank transmission.
[0110] Since the CoMP JT scheme and the single-cell SU-MIMO scheme
have a similar characteristic in that a UE receives high rank
transmission, the two communication schemes have the corresponding
relationship with each other and thus dynamic switching can be
easily performed. Here, dynamic switching refers to switching from
one mode to another mode without additional signaling from a BS. In
other words, during switching from the CoMP JT scheme to the
single-cell SU-MIMO scheme or from the single-cell SU-MIMO scheme
to the CoMP JT scheme, additional signaling may not be needed. In
the CoMP JT scheme, dynamic switching to the single-cell SU-MIMO
scheme may be expressed as fallback without additional signaling
from the CoMP JT scheme to the single-cell SU-MIMO scheme. Namely,
fallback from the CoMP JT scheme to the single-cell SU-MIMO scheme
refers to signal transmission to an associated UE only in one cell
and stop of signal transmission to an associated UE in the other
cells, while transmitting signals to one UE in two or more cells
according to the CoMP JT scheme. Such fallback may be regarded
operation according to the single-cell SU-MIMO scheme.
[0111] When multiple cells participate in CoMP JP, it is possible
to perform dynamic switching between CoMP JT schemes having
different transmission cells. For example, with respect to a UE
located at a common boundary of cells A, B, and C, dynamic
switching may be performed such that communication of the CoMP JT
scheme is performed in the cells A and B at any time point and
communication of the CoMP JT scheme is performed in the cells A and
C at another time point.
[0112] As another example, since CBF of the CoMP communication
scheme and MU-MIMO of the single-cell MIMO communication scheme
have something in common in that the both schemes generally perform
transmission of a low rank, the corresponding relationship of these
two communication scheme may be considered. More specifically, in
case of the CoMP CBF scheme, since signals for one UE are
transmitted from only one BS and a CoMP operation is mainly
performed with respect to a UE at a cell boundary, it is generally
difficult to use high rank. In addition, in the CBF scheme, a
cooperative cell should determine a beam direction which is not
used by a target UE of the CoMP operation. However, if a signal of
a high rank is transmitted to the corresponding UE, options for
selection of a beam direction which can be used in a cooperative
cell may become narrow. Accordingly, the CoMP CBF scheme generally
performs transmission of a low rank. In case of the single-cell
MU-MIMO scheme, since two or more UEs receive signals by sharing
spatial resources of one cell, a rank of each UE is generally set
to have a low value.
[0113] Since the CoMP CBF scheme and the single-cell MU-MIMO scheme
have similar characteristics in that a UE receives low rank
transmission, the two communication schemes have a corresponding
relationship with each other and thus dynamic switching can be
easily performed therebetween. In other words, during switching
from the CoMP CBF scheme to the single-cell MU-MIMO scheme or from
the single-cell MU-MIMO scheme to the CoMP CBF scheme, additional
signaling may not be needed. In the CoMP CBF scheme, dynamic
switching to the single-cell MU-MIMO scheme may be expressed as
fallback without additional signaling from the CoMP CBF scheme to
the single-cell MU-MIMO scheme. Namely, fallback from the CoMP CBF
scheme to the single-cell MU-MIMO scheme means that, for example,
during MIMO transmission to the plurality of UEs in a cell A,
operation (i.e. operation of the CoMP CBF scheme) is performed by
cooperation with a cell B such that a beam of the cell B is not
formed in the direction of the plurality of UEs receiving signals
from the cell, and thereafter, the cell A alone performs MIMO
transmission to the plurality of UEs without beamforming
cooperation of the cell B. Such fallback may be regarded operation
in the single-cell MU-MIMO scheme.
[0114] As still another example, CSL of the CoMP communication
scheme may have a corresponding relationship with CoMP JT of the
CoMP JP scheme to dynamically perform switching between these
communication schemes.
[0115] In addition, switching between one of the CoMP JT scheme and
the single-cell SU-MIMO scheme and one of the CoMP CBF scheme and
the single-cell MU-MIMO scheme may also be dynamically
performed.
[0116] Switching between the CoMP communication scheme and the
single-cell MIMO communication scheme, which have been described,
may be illustrated as in FIG. 10.
[0117] Meanwhile, it is proposed that switching between the CoMP
communication scheme and the single-cell MIMO communication scheme,
except for the corresponding relationship between the CoMP JT
scheme and the single-cell SU-MIMO scheme and the corresponding
relationship between the CoMP CBF scheme and the single-cell
MU-MIMO scheme, be non-dynamically performed. In other words,
switching between the CoMP scheme and the single-cell MIMO
communication scheme except for the corresponding relationship
between the above-described CoMP scheme and single-cell MIMO
communication scheme may be performed through a higher layer signal
(e.g. through RRC signaling). For instance, when switching to the
CoMP CBF scheme or the single-cell MU-MIMO scheme from the CoMP JT
scheme or the single-cell SU-MIMO scheme is performed, a higher
layer signal indicating such switching is transmitted to a UE from
a BS, and the UE may be semi-statically operated according to any
one of the two schemes by a corresponding signal.
[0118] As described above, it is possible to dynamically switch
between the CoMP communication scheme and the single-cell MIMO
communication scheme without additional signaling. To support this,
it may be considered to have common characteristics in CQI
transmission and feedback codebook use in the CoMP communication
scheme and single-cell MIMO communication scheme having the
corresponding relationship.
[0119] CQI Transmission
[0120] In the above-described communication schemes having a
corresponding relationship, it is proposed to apply the same
hypothesis when a UE calculates a CQI and/or an RI. Applying the
same hypothesis means that the same configuration and method are
applied when the CQI and/or the RI are calculated and transmitted.
Dynamic switching between the CoMP communication scheme and the
single-cell MIMO communication scheme can be easily performed by
calculating the CQI and/or RI according to the same hypothesis.
[0121] Hypothesis about CQI and RI calculation may include
periodic/aperiodic transmission, a transmission period in case of
periodic transmission, a frequency band for CQI calculation, a MIMO
transmission scheme, and a relationship between the CQI and the RI,
and the same hypothesis about these factors may be applied to the
communication schemes having a corresponding relationship. More
specifically, the CQI is calculated based on channel quality such
as a Signal-to-Noise Ratio (SNR) and may provide information about
a link adaptive parameter which can be supported by a UE at a given
time. The CQI may be calculated by a wideband feedback scheme in
which one CQI value for an entire system band is fed back, a
UE-selected subband feedback scheme in which a UE estimates channel
quality of each subband, selects a plurality of subbands having
good quality, and feeds back an average CQI value for the selected
subbands, and a higher layer configured subband feedback scheme in
which an individual CQI for each subband configured in a higher
layer is fed back. The RI may indicate information about the number
of layers recommended by a UE. In other words, the RI may indicate
the number of streams used for spatial multiplexing. The RI can be
fed back only when a UE operates in a MIMO mode using spatial
multiplexing. For example, the RI is not fed back in a single
antenna port mode or a transmit diversity mode. The RI is always
associated with more than one CQI feedback. Namely, a CQI which is
fed back is calculated under the assumption of a specific RI value.
Generally, since a channel rank varies slower than the CQI, the
number of RIs less than the number of CQIs may be fed back. For
example, the transmission period of the RI may be twice the
transmission period of the CQI/PMI. The RI is given for an entire
system band, and frequency selected RI feedback is not supported.
The transmission of uplink control information includes periodic
transmission and aperiodic transmission. Although the periodic
transmission is usually performed through a PUCCH, it may be
performed through a PUSCH. The aperiodic transmission is performed
by requesting a UE when a BS needs more accurate channel state
information. The aperiodic transmission is performed through a
PUSCH. The use of the PUSCH enables large capacity and precise
channel state reporting. If the periodic transmission and aperiodic
transmission collide, only the aperiodic transmission is
performed.
[0122] When a BS transmits signals to a UE by determining an MCS
etc. according to the feedback CQI, different CQI feedback methods
may be applied according to the characteristics of a communication
scheme. For example, in the CoMP JT scheme or the single-cell
SU-MIMO scheme, since signals are transmitted to one UE from a cell
or cells, a difference between channel quality measured and then
fed back by the UE and actually transmitted channel quality may be
insignificant. However, in the CoMP CBF scheme or the single-cell
MU-MIMO scheme, since signals are transmitted to a plurality of UEs
from a cell or cells and channel quality measured by one UE may be
influenced by a channel to another UE, there occurs a difference
between channel information measured and then fed back by the UE
and actually transmitted channel quality. In this case, even though
the BS determines an MCS etc. of a transmission signal based on the
feedback CQI, a new scheme for feeding back channel quality
correction information again to a cell or cells may be considered
in consideration of channel quality during actual signal
transmission.
[0123] Alternatively, a scheme for a UE to previously inform a cell
of channel quality correction information about single-cell MU-MIMO
may be considered. More specifically, when any UE feeds back a CQI
in single-cell SU-MIMO to a cell, the UE may feed back correction
information indicating how a CQI in MU-MIMO (i.e. considering other
UEs) is changed compared with the CQI in single-cell SU-MIMO, under
the assumption that the UE operates according to a single-cell
MU-MIMO scheme as a pair with another UE using specific precoding
information. Similarly, the UE may provide a CQI in the CoMP CBF
scheme or the single-cell MU-MIMO scheme to cells as correction
information based on a CQI in the CoMP JT scheme or the single-cell
SU-MIMO scheme.
[0124] Considering this, a conventional CQI calculation and
transmission method (i.e. a first hypothesis of CQI calculation)
may be applied to the CoMP JT scheme and the single-cell SU-MIMO
scheme and a new CQI calculation and transmission method (i.e. a
second hypothesis of CQI calculation) may be applied to the CoMP
CBF scheme and the single-cell MU-MIMO scheme.
[0125] The UE transmits the CQI and/or RI based on the same
hypothesis about considerations in transmitting the CQI and/or RI
in the CoMP communication scheme and single-cell MIMO communication
scheme having the corresponding relationship, thereby easily
performing dynamic switching between the CoMP communication scheme
and the single-cell MIMO communication scheme.
[0126] Feedback Codebook
[0127] To support dynamic switching according to the corresponding
relationship of the CoMP communication scheme and the single-cell
MIMO communication scheme, it is proposed to use the same feedback
codebook in the communication schemes having a mutual corresponding
relationship. Dynamic switching between the CoMP communication
scheme and the single-cell MIMO communication scheme can be easily
performed by using the same feedback codebook. Using the same
codebook means defining one codebook rather than defining separate
codebooks according to different communication schemes, and one
codebook may have codebook scalability which will be described
later.
[0128] Here, it is assumed that multi-cell channel information
feedback for a CoMP operation is configured by a combination of
channel information feedback for an individual coordinated cell.
Then a UE performing feedback for a CoMP operation may feed back
channel information of each CoMP coordinated cell using a feedback
codebook of a single-cell MIMO communication scheme corresponding
to (having a corresponding relationship) an associated CoMP
communication scheme which is semi-statically configured.
[0129] To support this, two different codebooks are defined. It is
proposed that one of the tow codebooks be used in the CoMP JT
scheme and the single-cell SU-MIMO scheme, and the other be used in
the CoMP CBF scheme and the single-cell MU-MIMO scheme.
[0130] For the CoMP JT scheme and the single-cell SU-MIMO scheme, a
feedback codebook optimized for a high rank may be used. In these
communication schemes, since one UE receives signals of multiple
layers, it is difficult to correctly receive the multiple layer
signals when a signal for one layer functions as interference with
other layers. Accordingly, it is necessary to maintain
orthogonality between a plurality of layers and thus a codebook
including unitary matrices (columns of which have orthogonality)
may be used. It may be assumed in a UE that a BS distinguishes
between different layers using precoding vectors having
orthogonality. As an example of such a codebook, a feedback
codebook defined in 3GPP LTE release-8 or an extended codebook
thereof may be used.
[0131] In the single-cell SU-MIMO scheme, feedback may be performed
based on a codebook-based transmission precoding hypothesis
(hypothesis using LTE release-8 codebook or an extended codebook
thereof) for a serving cell. In the CoMP JP (or CoMP JT) scheme,
feedback may be performed based on a transmission precoding
hypothesis about a serving cell and coordinated cells and relative
phase information between transmit PMIs (TPMIs) while a feedback
codebook used in the SU-MIMO scheme or an extended codebook thereof
is used.
[0132] Meanwhile, in the CoMP CBF scheme and the single-cell
MU-MIMO scheme, a feedback codebook optimized for a low rank may be
used. In this case, it is important to transfer accurate channel
information. However, since a precoding vector applied to each
layer does not need to have orthogonality (considering that other
layer signals are signals for other users), it is unnecessary for a
codebook to be configured by unitary matrices. By configuration of
a codebook of non-unitary matrices, the codebook can be designed
such that more accurate channel information can be transferred. In
addition, it is not assumed in the UE that the BS distinguishes
different layers using precoding vectors having orthogonality.
[0133] In the single-cell MU-MIMO scheme, feedback may be performed
based on a quantized channel or quantized effective channel for a
serving cell, and thus a reception process etc. may be used. In the
CoMP CBF scheme, feedback may be performed based on a quantized
channel or quantized effective channel for a serving cell and
coordinated cells.
[0134] In the CoMP CBF scheme, a feedback codebook may include a
non-unitary matrix when it is expressed in a matrix form, and may
include vectors not demanding orthogonality when it is expressed in
a column vector form.
[0135] In the CoMP CBF scheme and the single-cell MU-MIMO scheme, a
feedback codebook having higher granularity than a feedback
codebook used in the CoMP JT scheme and the single-cell SU-MIMO
scheme may be used to transfer more accurate channel information.
For example, the size of a feedback codebook may be increased (i.e.
a channel state can be fed back using more bits) or a hierarchical
codebook or adaptive codebook technique may be applied. The
hierarchical codebook technique means raising feedback accuracy
using different feedback codebooks (including multiple-resolution
codebooks having different resolution) every feedback time point.
The adaptive codebook technique means using a feedback codebook
obtained through modification such as multiplying a long-term
channel covariance matrix by a given basic feedback codebook.
[0136] Codebook Scalability
[0137] Codebook scalability means that a subset of a codebook used
in one of different communication schemes can configure a codebook
of another communication scheme while the same codebook is
basically used between different communication schemes. For
example, while the same codebook is defined and used in the
single-cell MIMO communication scheme and the CoMP communication
scheme, a codebook in the single-cell MIMO communication scheme may
be configured as a subset of a codebook used in the CoMP
communication scheme.
[0138] According to the present invention, code scalability is
applied to the CoMP communication scheme and single-cell MIMO
communication scheme having a mutual corresponding relationship and
facilitates dynamic switching therebetween.
[0139] More specifically, in the CoMP JP scheme, a precoding
codebook may reuse a single-cell SU-MIMO precoding codebook (e.g.
codebook defined in LTE release-8) to apply precoding for an
antenna port of each cell. Further, in the CoMP JP scheme,
potentially different phase adjustment values may be applied to
each cell.
[0140] A precoding codebook in the single-cell MU-MIMO scheme and a
feedback codebook in the CoMP CBF scheme may have scalability. For
example, the single-cell MU-MIMO feedback codebook and the CoMP CBF
feedback codebook may be the same codebook, or the single-cell
MU-MIMO precoding codebook may be a subset of the CoMP CBF feedback
codebook. Here, the feedback codebook used in the CoMP CBF scheme
may be a codebook including non-unitary matrices. In the CoMP CBF
scheme, when a plurality of vectors is fed back by a UE (e.g.
feedback for a high rank or feedback for both a serving cell and
coordinated cells), the plurality of vectors does not need to have
orthogonality.
[0141] Meanwhile, a precoding codebook in the single-cell SU-MIMO
scheme and a feedback codebook in the CoMP CBF scheme may have
scalability although the CoMP communication scheme and single-cell
MIMO communication scheme do not have a mutual corresponding
relationship. In other words, the single-cell SU-MIMO precoding
codebook may be a subset of the CoMP CBF feedback codebook. More
specifically, although the CoMP CBF feedback codebook may be a
codebook including non-unitary matrices, the single-cell SU-MIMO
precoding codebook may be a subset including only unitary matrices
in the CoMP CBF feedback codebook.
[0142] As described previously, the single-cell MU-MIMO feedback
codebook and the single-cell SU-MIMO precoding codebook may be
configured by a subset of the CoMP CBF feedback codebook.
Furthermore, the single-cell MU-MIMO feedback codebook and the
single-cell SU-MIMO precoding codebook may be configured by the
same codebook.
[0143] From this viewpoint, since the single-cell SU-MIMO scheme,
CoMP JP scheme, single-cell MU-MIMO scheme, and CoMP CBF scheme may
use the same codebook or an extended codebook thereof, it may be
said that a feedback codebook between different communication
schemes is dynamically configured.
[0144] Feedback Mode
[0145] Generally, although a UE operating according to the
single-cell MIMO communication scheme transmits feedback
information only to one cell, a UE operating according to the CoMP
communication scheme requires that feedback information be
transmitted to a plurality of cells. It may be difficult to use a
feedback mode in the single-cell MIMO communication scheme for the
purpose of feedback in the CoMP communication scheme. However, it
may be considered that feedback in the CoMP communication scheme is
configured in an extended form of feedback in the single-cell MIMO
communication scheme.
[0146] Further, since high rank transmission is generally performed
in the single-cell SU-MIMO scheme and the CoMP JP scheme, a
feedback mode thereof may consider feedback for high rank
transmission. On the other hand, since low rank transmission is
generally performed in the single-cell MU-MIMO scheme and the CoMP
CBF scheme, a feedback mode thereof may consider feedback for low
rank transmission.
[0147] According to the present invention, in the CoMP
communication scheme and single-cell MIMO communication scheme
having a mutual corresponding relationship may have scalability or
a common feedback mode.
[0148] More specifically, the single-cell SU-MIMO scheme and the
CoMP JP scheme may have a scalable feedback relationship. Namely,
feedback information in the single-cell SU-MIMO scheme may be a
subset of feedback information of the CoMP JP scheme. Moreover, the
single-cell SU-MIMO scheme and the CoMP JP scheme may have a common
feedback mode. In other words, the single-cell SU-MIMO scheme may
be regarded a special case of the CoMP JP scheme, a CoMP set size
of which is 1. A BS may inform a UE of information about the CoMP
set size.
[0149] The single-cell MU-MIMO scheme and the CoMP CBF scheme may
have a scalable feedback relationship. Namely, feedback information
in the single-cell MU-MIMO scheme may be a subset of feedback
information in the CoMP CBF scheme. The single-cell MU-MIMO scheme
and the CoMP CBF scheme may have a common feedback mode. In other
words, the single-cell MU-MIMO scheme may be regarded a special
case of a CoMP CBF scheme, a CoMP set size of which is 1. A BS may
inform a UE of information about the CoMP set size.
[0150] As described above, since the scalability or commonness of a
feedback mode between the CoMP communication scheme and single-cell
MIMO communication scheme having a corresponding relationship are
provided, dynamic switching therebetween is facilitated.
[0151] Meanwhile, semi-static feedback mode switching may be
applied between the CoMP communication scheme and single-cell MIMO
communication scheme which do not have a mutual corresponding
relationship. That is, feedback mode switching between one of the
single-cell SU-MIMO scheme and the CoMP JP scheme and one of the
single-cell MU-MIMO scheme and the CoMP CBF scheme may be
semi-statically performed.
[0152] Transmission Mode
[0153] In the aforementioned CoMP communication scheme and
single-cell MIMO communication scheme, various MIMO transmission
modes may be used in some cases. A MIMO transmission mode may be
indicated through scheduling signaling (PDCCH DCI format) and
various DCI formats may be used according to various MIMO
transmission modes. Generally, when different MIMO transmission
modes are used according to various communication schemes,
different DCI formats for indicating the transmission modes may be
used.
[0154] According to the present invention, it is proposed to
perform dynamic transmission mode switching between the CoMP
communication scheme and single-cell MIMO communication scheme
having a mutual corresponding relationship. In other words,
transmission modes may be switched between the CoMP communication
scheme and single-cell MIMO communication scheme having a
corresponding relationship without additional signaling.
[0155] More specifically, dynamic transmission mode switching may
be applied between the single-cell SU-MIMO scheme and the CoMP JP
scheme. Alternatively, a single transmission mode may be applied
between the single-cell SU-MIMO scheme and the CoMP JP scheme. When
the single transmission mode is used in different communication
schemes, even if a communication scheme is changed, the
corresponding single transmission mode is not recognized by a UE
and such a property may be called to be transparent. Namely, a
transmission mode between the single-cell SU-MIMO scheme and the
CoMP JP scheme may be called to be transparent.
[0156] In addition, dynamic transmission mode switching or a single
transmission mode may be applied (i.e. transparent) between the
single-cell MU-MIMO scheme and the CoMP CBF scheme.
[0157] Meanwhile, transmission mode switching between one of the
single-cell SU-MIMO scheme and the CoMP JP scheme and one of the
single-cell MU-MIMO scheme and the CoMP CBF scheme may be
semi-statically performed.
[0158] On the other hand, dynamic transmission mode switching is
applicable or a single transmission mode is applicable (i.e.
transparent) between the single-cell SU-MIMO scheme, CoMP JP
scheme, single-cell MU-MIMO scheme, and CoMP CBF scheme, using a
Dedicated Reference Signal (DRS).
[0159] FIG. 11 is a flowchart of a dynamic switching method between
a CoMP communication mode and a single-cell MIMO communication mode
according to an exemplary embodiment of the present invention.
[0160] In step S1110, a UE may operate in a first communication
mode. The first communication mode may be one of a CoMP
communication mode and a single-cell MIMO communication mode. Here,
the UE may generate and transmit channel feedback information to
cells. A first feedback codebook may be used to generate the
feedback information.
[0161] In step S1120, the UE may switch from the first
communication mode to a second communication mode. The second
communication mode is a communication mode having a corresponding
relationship with the first communication mode. If the first
communication mode is one of the CoMP communication mode and the
single-cell MIMO communication mode, the second communication mode
may be determined as the other one. In other words if the first
communication mode is the CoMP communication mode, then the second
communication mode may be the single-cell MIMO communication mode
having a corresponding relationship with the CoMP communication
mode. Alternatively, if the first communication mode is the
single-cell MIMO communication mode, then the second communication
mode may be the CoMP communication mode having a corresponding
relationship with the single-cell MIMO communication mode. Since
the first and second communication modes are communication modes
having a corresponding relationship, a UE may perform communication
mode switching without additional signaling from a BS. This can be
said to be dynamic switching of a communication mode as described
above.
[0162] More specifically, a corresponding relationship of the first
communication mode and the second communication mode may be
configured between the CoMP communication scheme supporting high
rank transmission and the single-cell MIMO communication scheme
supporting high rank transmission. That is, the corresponding
relationship of the first and second communication modes may be
configured between the CoMP JT scheme and the single-cell SU-MIMO
scheme. Alternatively, the corresponding relationship of the first
communication mode and the second communication mode may be
configured between the CoMP communication scheme supporting low
rank transmission and the single-cell MIMO communication scheme
supporting low rank transmission. In other words, the corresponding
relationship of the first and second communication modes may be
configured between the CoMP CBF scheme and the single-cell MU-MIMO
scheme.
[0163] In step S1130, the UE may operate according to the second
communication mode. Here, the UE may generate and transmit channel
feedback information to a cell or cells. A second feedback codebook
may be used to generate the feedback information.
[0164] The first feedback codebook and the second feedback codebook
may be the same feedback codebook. Alternatively, one of the first
feedback codebook and the second feedback codebook may be
configured by a subset of the other one. For example, if the first
communication mode is the CoMP communication mode and the second
communication mode is the single-cell MIMO communication mode, then
the second feedback codebook may be configured by a subset of the
first feedback codebook. (Alternatively, if the first communication
mode is the single-cell MIMO communication mode and the second
communication mode is the CoMP communication mode, then the first
feedback codebook may be configured by a subset of the second
feedback codebook.) Thus, feedback information in the single-cell
MIMO communication mode may be configured by a subset of feedback
information in the CoMP communication mode.
[0165] Moreover, if a corresponding relationship of the first
communication mode and the second communication mode is configured
between the CoMP JT scheme and the single-cell SU-MIMO scheme, the
first feedback codebook and the second feedback codebook may
include unitary matrices. Meanwhile, if a corresponding
relationship of the first communication mode and the second
communication mode is configured between the CoMP CBF scheme and
the single-cell MU-MIMO scheme, the first feedback codebook and the
second feedback codebook may include non-unitary matrices. A
feedback codebook used in the CoMP CBF scheme and the single-cell
MU-MIMO scheme may have higher granularity than a feedback codebook
used in the CoMP JT scheme and the single-cell SU-MIMO scheme. The
feedback codebook having higher granularity may be composed of a
feedback codebook of greater size or may be configured using the
aforementioned hierarchical codebook or adaptive codebook
technique.
[0166] The first feedback information and the second feedback
information may include CQI and/or RI information. The CQI and/or
RI information may be generated based on the same hypothesis in the
first communication mode and second communication mode having a
corresponding relationship (i.e. single-cell MIMO communication
mode and CoMP communication mode having a corresponding
relationship). In addition, the same MIMO transmission scheme may
be used in the first communication mode and second communication
mode having a corresponding relationship (i.e. single-cell MIMO
communication mode and CoMP communication mode having a
corresponding relationship).
[0167] In the dynamic switching method of the communication modes
according to an exemplary embodiment of the present invention
described with reference to FIG. 11, details may be achieved by the
above-described various proposals of the present invention.
[0168] FIG. 12 is a diagram illustrating the configuration of an
exemplary embodiment of a UE according to the present
invention.
[0169] A UE 1210 may include a reception module 1211, a
transmission module 1212, a processor 1213, a memory 1214, and a
plurality of antennas 1215. The plurality of antennas means that
the UE supports a MIMO scheme. The UE 1210 may perform multi-cell
communication with a plurality of BSs 1221 and 1222.
[0170] The reception module 1211 may receive various signals, data,
and information in downlink from the BSs. The transmission module
1212 may transmit various signals, data, and information in uplink
to the BSs. The processor 1213 may control overall operation of the
UE 1210. Especially, the processor 1213 may control transmission
and reception of various signals, data, and information through the
reception module 1211 and the transmission module 1212.
[0171] In the exemplary embodiment of the present invention, the UE
1210 may perform dynamic switching of a communication mode. To this
end, the processor 1213 of the UE 1210 may generate first feedback
information according to a first communication mode and generate
second feedback information according to a second communication
mode. The processor 1213 of the UE 1210 may be configured to
transmit, through the transmission module, the first feedback
information when the UE 1210 operates in the first communication
mode and the second feedback information when the UE 1210 operates
in the second communication mode. The processor 1213 may be
configured to perform switching between the first communication
mode and the second communication mode. The first and second
communication modes are communication modes having a corresponding
relationship. The first communication mode may be one of the CoMP
communication and the single-cell MIMO communication mode and the
second communication mode may be the other one. The processor 1213
may perform switching between the first communication mode and the
second communication mode without depending on signaling from the
BSs.
[0172] In relation to the configuration of the UE 1210, matters
described in the various embodiments of the present invention may
be applied and a repetitive description is omitted for clarity.
Namely, details related to UE operation described in this document
may be achieved in each element of the UE.
[0173] The processor 1213 of the UE 1210 performs an operational
processing function for information received by the UE and
information to be transmitted to an external device. The memory
1214 may store the processed information for a given time period
and may be replaced with an element such as a buffer (not
shown).
[0174] The above-described embodiments of the present invention can
be implemented by various means, for example, hardware, firmware,
software, or combinations thereof.
[0175] In a hardware configuration, the method according to the
embodiments of the present invention may be implemented by one or
more Application Specific Integrated Circuits (ASICs), Digital
Signal Processors (DSPs), Digital Signal Processing Devices
(DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate
Arrays (FPGAs), processors, controllers, microcontrollers,
microprocessors, etc.
[0176] In a firmware or software configuration, the method
according to the embodiments of the present invention may be
achieved by a module, a procedure, a function, etc. performing the
above-described functions or operations. Software code may be
stored in a memory unit and executed by a processor. The memory
unit is located at the interior or exterior of the processor and
may transmit data to and receive data from the processor via
various known means.
[0177] The detailed description of the exemplary embodiments of the
present invention has been given to enable those skilled in the art
to implement and practice the invention. Although the invention has
been described with reference to the exemplary embodiments, those
skilled in the art will appreciate that various modifications and
variations can be made in the present invention without departing
from the spirit or scope of the invention described in the appended
claims. For example, those skilled in the art may use each
construction described in the above embodiments in combination with
each other. Accordingly, the invention should not be limited to the
specific embodiments described herein, but should be accorded the
broadest scope consistent with the principles and novel features
disclosed herein.
[0178] The present invention may be carried out in other specific
ways than those set forth herein without departing from the spirit
and essential characteristics of the present invention. The above
detailed description is therefore to be construed in all aspects as
illustrative and not restrictive. The scope of the invention should
be determined by the appended claims and their legal equivalents,
not by the above description, and all changes coming within the
meaning and equivalency range of the appended claims are intended
to be embraced therein. The invention should not be limited to the
specific embodiments described herein, but should be accorded the
broadest scope consistent with the principles and novel features
disclosed herein. Also, claims that are not explicitly cited in the
appended claims may be presented in combination as an exemplary
embodiment of the present invention or included as a new claim by
subsequent amendment after the application is filed.
INDUSTRIAL APPLICABILITY
[0179] The exemplary embodiments of the present invention as
described above are applicable to a variety of mobile communication
systems.
* * * * *